System and method of mitigating effects of component deflection in a probe card analyzer

ABSTRACT

A system and method of mitigating the effects of component deflections in a probe card analyzer system may implement three-dimensional comparative optical metrology techniques to model deflection characteristics. An exemplary system and method combine non-bussed electrical planarity measurements with fast optical planarity measurements to produce “effectively loaded” planarity measurements.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. provisionalapplication Ser. No. 60/454,574, filed Mar. 14, 2003, entitled“MITIGATING THE EFFECTS OF PROBE CARD/FIXTURE AND METROLOGY BASEDEFLECTION IN A PROBE CARD ANALYZER,” the disclosure of which is herebyincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

Aspects of the present invention relate generally to the field of probecard analyzers, and more particularly to a system and method ofmitigating the effects of component deflections in a probe card analyzersystem.

BACKGROUND OF THE INVENTION

Traditional probe card analyzers measure probe planarity by electricalmeans, and generally measure probe alignment by optical means.Electrical planarity measurements are typically made by slowly bringinga conductive contact surface into contact with the probes on a probecard. In that regard, the conductive contact surface is moved toward theprobe card; the conductive surface first makes contact with the probethat extends furthest from the probe card surface (the “lowest” probe),and finally makes contact with the probe that extends least from theprobe card surface (the “highest” probe). In this context, the terms“lowest” and “highest” are not necessarily intended to imply a verticalorientation. The process of moving the conductive contact surface fromfirst to last contact point and beyond is generally referred to in theart as “overtravel,” since the first probe to make contact with theconductive contact surface is loaded beyond the point of first contact.

As probes are “overtraveled,” the contact loads increase. For probecards implementing many probes, these contact loads can become quitehigh, and are capable of producing deflections in system components thatmay significantly impact the accuracy of measurement results.

In a typical probe card analyzer system taking electrical planaritymeasurements across a single large contact surface, the deflection ofthe probe card, the probe card fixture, the metrology frame, or somecombination thereof, may become an integral part of the planaritymeasurement itself. This is due to the fact that the loads arising fromcontact with lower probes cause deflection, which in turn increases theapparent planarity of higher probes.

Optical planarity measurements, on the other hand, may be made byoptically scanning the tips of free-hanging probes. Under suchconditions (i.e., free-hanging probes with no overtravel), contact loadsare never created, and hence cannot cause component deflections orflexure of any kind. Accordingly, such optical planarity measurementsmay differ from electrical planarity measurements, even with respect tothe same probe card under analysis. Additionally, optical methodologiesgenerally enjoy a speed advantage over electrical planarity evaluativemethods. The rapidity of optical planarity measurements and techniquesmake such optical technology attractive; it is highly desirable todevelop a method of producing equivalent electrical planarity analysisbased upon or benefiting from fast optical measurements.

Currently implemented systems and methods are deficient in thattraditional methodologies do not accurately correlate optical planaritymeasurements, which are made in the absence of contact loads, toelectrical planarity measurements, which are made in the presence of,and are influenced by, such contact loads.

SUMMARY

Aspects of the present invention overcome the foregoing and othershortcomings of conventional technology, providing a system and methodof mitigating the effects of component deflections in a probe cardanalyzer system. An exemplary system and method combine non-bussedelectrical planarity measurements with fast optical planaritymeasurements to produce “effectively loaded” planarity measurements.

In accordance with one exemplary embodiment, a method of obtainingplanarity measurements in a probe card analysis system comprises:computing planarity effects due to fiducial plate deflection; combiningplanarity effects due to probe card deflection and due to probe cardfixture deflection; and responsive to the computing and the combining,calculating a load compensated planarity for the probe card. In someimplementations, the method may further comprise accounting forplanarity effects due to stage deflection; additionally, the calculatingmay be further responsive to the accounting. In accordance with oneaspect of an exemplary method, the accounting comprises utilizing adistance sensor proximate to the stage deflection.

The computing may comprise utilizing an optical metrology technique,such as a three-dimensional optical metrology method. In someembodiments, the utilizing an optical metrology technique comprises:acquiring image data of a fiducial on the fiducial plate; responsive tothe acquiring, identifying deflection data values representative of adeflection of the fiducial plate; and responsive to the identifying,providing correction data values enabling a first order correction ofthe deflection. In some alternative embodiments, the method furthercomprises: further identifying rate data values representative of a rateof deflection of the fiducial plate; and responsive to the furtheridentifying, providing additional correction data values enabling asecond order correction of the deflection.

In accordance with another aspect of some embodiments of a planaritymeasuring method, the combining comprises: obtaining measurements ofoptical planarity and electrical planarity for the probe card; measuringfiducial plate deflection at first electrical contact; and responsive tothe obtaining and the measuring, computing a combined deflection valuefor the probe card and the probe card fixture.

As set forth below with specific reference to exemplary embodiments, amethod of obtaining a combined deflection measurement for deflections ofa probe card and a probe card fixture may comprise: obtainingmeasurements of optical planarity and measurements of electricalplanarity for all non-bussed probes; identifying fiducial platedeflection at first electrical contact at all non-bussed probelocations; and responsive to the obtaining and the identifying,computing a combined deflection attributable to deflection of the probecard and deflection of the probe card fixture. Some such methods aredisclosed as further comprising acquiring stage deflection measurementsat proximal sensor locations, and wherein the computing is furtherresponsive to the acquiring; alternatively, the stage deflectionmeasurements may be assumed to be zero in some applications.

In accordance with some embodiments of a method of obtaining a combineddeflection measurement, the operation of identifying fiducial platedeflection comprises: selectively positioning an imaging apparatus toacquire optical data at a selected non-bussed probe location; acquiringthe optical data when a non-bussed probe makes contact with the fiducialplate at the selected non-bussed probe location; and responsive to theacquiring, measuring the fiducial plate deflection at the selectednon-bussed probe location. The foregoing selectively positioning,acquiring, and measuring may be selectively repeated for a differentselected non-bussed probe location.

Alternatively, the operation of identifying fiducial plate deflectionmay comprise computing the fiducial plate deflection as a function offull overtravel plate deflection at a particular probe location and ofoptical planarity; the computing may comprise utilizing a twodimensional interpolation calculation to approximate deflections atother probe locations.

The foregoing and other aspects of the disclosed embodiments will bemore fully understood through examination of the following detaileddescription thereof in conjunction with the drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram illustrating components of oneembodiment of a probe card analyzer system.

FIG. 2 is a simplified block diagram illustrating exemplary z-stagedeflection under contact loading due to overtravel.

FIG. 3 is a simplified block diagram illustrating exemplary fiducialplate deflection under contact loading due to overtravel.

FIG. 4 is a simplified block diagram illustrating one embodiment of atechnique for measuring fiducial plate deflection.

FIG. 5 is a simplified flow diagram illustrating the general operationof one embodiment of a method of obtaining planarity measurements in aprobe card analysis system.

DETAILED DESCRIPTION

By way of general background, it will be appreciated that the approachto obtaining optical planarity measurements generally known in the artand set forth by way of example herein is that of three-dimensionalcomparative metrology using a substantially transparent fiducialsubstrate, e.g., a glass, acrylic, quartz, or other suitably transparentfiducial plate as set forth in more detail below. While an exemplarythree-dimensional comparative metrology technique is described below,other optical planarity assessment methods may be known or developed inaccordance with generally known principles. The following description isprovided by way of example only and not by way of limitation; thepresent disclosure is not intended to be limited to any particularmethod of performing an optical planarity analysis.

FIG. 1 is a simplified block diagram illustrating components of oneembodiment of a probe card analyzer system. As is generally known in theart, system 100 may comprise a metrology frame 110 to which othercomponents are mounted. Specifically, exemplary system 100 generallycomprises a plate reference surface 121 configured and operative tocarry or otherwise to support a substantially transparent fiducial plate122, a probe card 132 attached to or otherwise supported by a probe cardfixture 131, and a z-stage 140 configured and operative to providerelative movement (along an axis, z, e.g., vertically in FIG. 1) betweenfiducial plate 122 and probe card 132. In some embodiments, one or moresensors, such as z-sensor 141, for example, may measure the relativedistance between probe card fixture 131 and plate reference surface 121.

Typically, fiducial plate 122, in addition to being substantiallytransparent as set forth in more detail below, is also electricallyconductive to enable electrical planarity measurements.

Optics assembly 150 may be employed to acquire image data (e.g., visualor optical data) of one or more probes 133 through substantiallytransparent fiducial plate 122. Accordingly, the term “substantiallytransparent” as used herein generally refers to the quality of allowingtransmission of sufficient energy in at least a portion of theelectromagnetic spectrum, such as the visible wavelengths of thespectrum, for example, to allow optics assembly 150 to acquire suchimages or optical data through fiducial plate 122. It will beappreciated that various factors may affect characterization of aparticular fiducial plate 122 as “substantially transparent” in thiscontext. For example, “substantial” transparency may be affected orinfluenced by some or all of the following, among other factors:transmission properties and attenuation properties (such as therefractive index, the presence and density of any occlusions, etc.) ofthe material used to construct fiducial plate 122; the thickness offiducial plate 122 along the optical axis of optics assembly 150; thetype (frequency and amplitude, for example) of energy impinging upon orpassing through fiducial plate 122; the capabilities and sensitivity ofoptics or imaging hardware employed at optics assembly 150; and thelike. In some embodiments, fiducial plate 122 may be constructed ofglass, acrylic, quartz, or a similar material substantially transparentto electromagnetic energy in a predetermined or desired portion of thespectrum.

It will be appreciated that system 100 may also comprise various motors,actuators, positional sensors, and the like (not shown in FIG. 1)configured and generally operative to control relative positioning andorientation of the various components such as z-stage 140, x-stage 160,y-stage (not shown), optics assembly 150, fiducial plate 122, and probecard 132. For example, the operational focal length of opticalequipment, lens arrangements, sensors (such as a charge-coupled device(CCD) or complementary metal-oxide semiconductor (CMOS) detector), orother imaging hardware utilized at optics assembly 150 may affect theoptimum or desired distance (in the z dimension) between optics assembly150 and fiducial plate 122. Similarly, selective positioning of opticsassembly 150 relative to fiducial plate 122, probe card 132, or both, ineither or both of the x and y directions may be required or desired. Inmany applications, precise three-dimensional positioning and orientationof the various components may be influenced or controlled by one or morecomputers, micro-controllers, programmable logic controllers, or otherelectronic or electromechanical components such as stepper motors, wormgears, precision actuators, and the like. Numerous hardware and softwareconfigurations suitable for this purpose are generally known in the art,and are susceptible of many variations and modifications. The presentdisclosure is not intended to be limited by any particular combinationof hardware elements and software modules operative selectively tomanipulate the components of system 100 in three-dimensional space.

Additionally, various components illustrated in the exemplary FIG. 1embodiment may be coupled to one or more computers or other processingcomponents. Specifically, a data processing component comprisinghardware and software may be configured and operative to receiveacquired image data and to compute planarity, for example, or to performother operations. Such a data processing component may additionally beoperative to command or request movement or rotation of various systemcomponents to correct for deflections as set forth in more detail below.The present disclosure is not intended to be limited by any particulardata processing hardware or software implementation, controlelectronics, feedback mechanisms, and the like.

As is generally known in the art, one factor underlying the superiorspeed and efficiency of optical planarity analyses over electricalplanarity analytical methodologies is the rapidity and efficiency withwhich the planarity of bussed probes can be measured using the opticaltechnology.

In some embodiments, a system and method constructed and operative inaccordance with the present disclosure combine non-bussed electricalplanarity measurements with fast optical planarity measurements toproduce “effectively loaded” planarity measurements. Specifically,aspects of the present invention are related to acquiring fastmeasurements of planarity that incorporate the effects of deflectionunder load that are present in typical electrical planaritymeasurements. Furthermore, exemplary approaches as outlined herein alsoproduce useful measurements of the combined deflection under load ofprobe card 132 and probe card fixture 131.

As contemplated herein, and further by way of background, the followingterminology will be used to describe various methods for measuringplanarity:

“electrical planarity” generally refers to electrical planaritymeasurements of non-bussed probes acquired in a loaded condition (i.e.,under contact load);

“optical planarity” or “unloaded planarity” generally refer to opticalplanarity measurements of all probes acquired in a no-load condition(i.e., under no contact load); and

“loaded planarity” generally refers to hybrid planarity measurements ofall probes acquired under load; in this context, load planaritymeasurements may be derived from a combination of fast optical and fastnon-bussed electrical planarity measurements. These measurementsgenerally may incorporate the effects of deflection under load, andhence may be related to or correlated with “electrical planarity”measurements.

In order to calculate loaded planarity, a determination may first bemade of the magnitude of deflections or flexures associated with varioussystem components; as set forth in general above, these deflections orflexures may occur during the measurement of electrical planarity whenone or more probes are subjected to loading as a result of an overtravelcondition. Specifically, such deflections may include some or all of thefollowing, without limitation: deflection of z-stage 140; deflection offiducial plate 122; and deflection of probe card 132, fixture 131, orboth.

Stage Deflection Measurement Effects

As set forth above, electrical planarity is conventionally measured byslowly moving, or “overtraveling,” a reference surface (such as platereference surface 121) relative to a reference surface 135 associatedwith probe card fixture 131. In the case of a probe card analyzer (suchas indicated by reference numeral 100 in FIG. 1) that measures planarityoptically via comparative metrology, an appropriate reference surface istypically plate reference surface 121. Planarity for probe card 132 maybe recorded as the location of z-stage 140 (along the z-axis) relativeto plate reference surface 121 at the point where the lowest probe 133first makes electrical contact with fiducial plate 122. This stagelocation (in the z dimension) generally is considered to represent thelocation of plate reference surface 121 relative to reference surface135 of probe card fixture 131.

FIG. 2 is a simplified block diagram illustrating exemplary z-stagedeflection under contact loading due to overtravel. As illustrated inFIG. 2, a problem may arise as loads develop during overtravel.Specifically, z-stage 140 may tend to deflect in the z direction, flexabout one or more axes, or otherwise to deform relative to referencesurface 135 of fixture 131 due to structural compliance; additionally oralternatively, as addressed below, flexure or other deformation mayoccur in fixture 131, probe card 132, or both due to the same forcesexerted by the contact loading on probes 133. By way of example, theleft side of FIG. 2 illustrates a deflection of plate reference surface121 relative to reference surface 135 of probe card fixture 131. If abase-line or tare z-position of stage 140 that is used to inferplanarity is taken from a remote measurement that neither observes noraccounts for such deflection effects (e.g., a measurement acquired froma motor shaft encoder near the base of metrology frame 110), error maybe introduced into the planarity measurement.

One exemplary mechanism which may effectively eliminate the foregoingerror employs a direct measurement acquired as close as possible toplate reference surface 121 and reference surface 135 associated withprobe card fixture 131. In that regard, the FIG. 2 embodiment isillustrated as employing a direct measurement sensor (z-sensor 141)appropriately disposed proximate both plate reference surface 121 andreference surface 135 associated with probe card fixture 131. Electricalplanarity measurements based upon, or taking into account, theseproximal sensor measurements may significantly reduce errors induced bydeflection of stage 140.

Fiducial Surface Deflection

Under load from probes 133 which have been overtraveled, fiducial plate122 may deflect, flex, warp, or otherwise deform. Such deflectiontypically has two primary components: rigid body deflection of fiducialplate 122 due to compliance at its supports; and bending deflection dueto compliance of fiducial plate 122 itself. Such deflection may resultin reduced, and potentially non-uniform, overtravel of one or moreprobes 133 over the probe array. In that regard, FIG. 3 is a simplifiedblock diagram illustrating exemplary fiducial plate deflection undercontact loading due to overtravel.

In accordance with the exemplary embodiment, a system and method as setforth herein may accurately measure the amount of deflection that hasoccurred in the area of fiducial plate 122 that actually contacts thearray of probes 133; accordingly, commanded overtravel may becompensated to nullify or to mitigate undesirable effects of thequantified deflection. Specifically, net resultant overtravel mayclosely approximate desired overtravel. It will be appreciated that theonly portion of deflection remaining uncompensated may be deflection offiducial plate 122 within the area actually making contact with thearray of probes 133. In practice, this component of deflection is muchless significant than the other deflection components that areidentified, and may thus be considered negligible.

As set forth above, the exemplary optical metrology techniques describedherein are generally three-dimensional comparative metrology analysesemploying or comprising stereoscopic imaging processes and asubstantially transparent fiducial plate 122. In addition to measuringprobe planarity and alignment, these optical analytical methodologiesmay also be capable of measuring deflection of fiducial plate 122relative to optics assembly 150.

FIG. 4 is a simplified block diagram illustrating one embodiment of atechnique for measuring fiducial plate deflection. In one imagingoperation, a fiducial grid network disposed on, or incorporated in thestructure of, fiducial plate 122 may be imaged from two perspectives.This imaging operation may result in acquisition of visual or otherimage data of the fiducial grid in a no-load situation, i.e., fiducialplate 122 is not under loading for purposes of this imaging process. Theposition of the fiducial array (in a no-load condition) may be measuredfrom each imaging perspective.

In another imaging operation, a load (such as may be expected duringovertravel in a probe analysis application, for example) may be appliedto fiducial plate 122; as set forth above, fiducial plate 122 maydeflect under such a load. The fiducial grid network may then be imaged,again from two perspectives. In some applications, including theexemplary embodiment illustrated in FIG. 4, these perspectives maycorrespond to those employed in the no-load imaging process;alternatively, in some more sophisticated imaging techniques, one orboth perspectives may differ from the perspectives used for the no-loadimaging process. Based upon this loaded imaging operation (i.e.,acquisition of visual or other image data), measurements may then betaken of the grid structure (in the loaded condition) from each imagingperspective.

It will be appreciated that the order in which the foregoing imagingoperations are conducted may not be important, or may be of onlytangential importance; in some applications, either the loaded or theno-load condition may be imaged first. In some exemplary embodiments,the imaging processes may be iterated or alternated one or more times toprevent calibration errors or to mitigate the effects thereof. Asillustrated in FIG. 4, fiducial plate 122 is deflected a distance,δ_(z). Changes in apparent location (e.g., in the loaded condition) ofone or more elements of the fiducial grid relative to the originallocation (e.g., in the no-load condition) may be expressed as δ_(y0) andδ_(y1), for each respective perspective. This geometry is depicted inFIG. 4, where the z axis is vertical and the y axis is horizontal in theplane of the figure. The viewing angle of optics assembly 150 off normalfrom each perspective is defined by the angle θ.

Given the geometry in FIG. 4, it is possible to compute the deflectionin fiducial plate 122 relative to the no-load condition via Equation(1):δ_(z)=(δ_(y0)+δ_(y1))/2 tan θ  (1)

Individual deflections may be mapped over the area of fiducial plate 122that is in contact with probes 133 to produce a set of measurementsrepresenting a number, n, of deflections over the contact area, as setforth below in Equation (2)p _(1i)=(x _(i) , y _(i), δ_(g1i))(i=1, 2, . . . , n)  (2)where x_(i) and y_(i) are the x and y locations of the deflectionmeasurement, and δ_(g1i) is the measured deflection (in the z direction)in fiducial plate 122. It is noted that the x axis is normal to theplane of FIG. 4.

Individual points, p_(1i), may be fit to a best-fit plane by variousmethods such as a linear least squares technique, for example, or someother suitable statistical methodology. From the plane fit, all of thefollowing physical characteristics fiducial plate 122 may be extracted:the deflection at the center (δ_(g1center)); the pitch angle about the xaxis, θ_(g1); and the roll angle about the y axis, Φ_(g1).

In accordance with the foregoing plane fit or a similar quantitativedeflection analysis operation, z-stage 140 may be manipulated orotherwise controlled to perform an incremental move in z, pitch, roll,or some combination thereof, to perform a first order correction formeasured deflections. Such an incremental move or positional adjustmentmay be made relative to the nominal overtravel position, and maygenerally be defined as set forth in Equations 3–5 below:Δz _(1cmd)=−δ_(g1center)  (3)θ_(1cmd)=−θ_(g1)  (4)Φ_(1cmd)=−Φ_(g1)  (5)where axial rotations are performed about the center of fiducial plate122.

These incremental moves or adjustments may have the effect ofestablishing a first order correction for deflection effects. In manycases, this first order correction will be sufficient to accommodate thedominant deflection characteristics, to correct for any effects causedthereby, and to model a desired level of uniform overtravel. Due largelyto flexure, deformation, or other material deflection or compliance, itis possible that the full extent of the commanded or desired incrementalmove (whether z translation or x or y rotation) may not be realized insome applications.

In that regard, it will be appreciated that any deviation from theforegoing commanded or desired adjustment generally represents a secondorder deflection error. If a higher level of accuracy (than thatprovided by the first order correction set forth above) in compensationis desired, the deflection rate of fiducial plate 122 may also beprecisely identified; a second incremental move or adjustment may thenenable elimination or minimization of such second order error effects.In some applications, for example, a second order correction may beaccomplished by measuring deflection of fiducial plate 122 over the samearea as measured prior to the first incremental move. This seconddeflection analysis may allow acquisition of a set of measurements asexpressed below in Equation (6):p _(2i)=(x _(i) , y _(i), δ_(g2i))(i=1, 2, . . . , n)  (6)

Again, these measurements, p_(2i), may be fit to a best-fit plane, suchas with a linear least squares technique or other suitable statisticalmechanism, to identify the central deflection and rotations of fiducialplate 122 (δ_(g2center), θ_(g2), and Φ_(g2)). The second ordertranslational and rotational deflection rates may be computed viaEquations (7–9):f _(z)=(δ_(g2center)−δ_(g1center))/δ_(g1center)  (7)f _(θ)=(θ_(g2)−θ_(g1))/θ_(g1)  (8)f _(Φ)=(Φ_(g2)−Φ_(g1))/(Φ_(g1)  (9)

An additional incremental overtravel command, relative to the nominalovertravel position (i.e., no deflection compensation position), maythen be expressed as follows in Equations (10–12):Δz _(1cmd)=−δ_(g1center)[1/(1−f _(z))]  (10)θ_(1cmd)=−θ_(g1)[1/(1−f _(θ))]  (11)Φ_(1cmd)=−Φ_(g1)[1/(1−f _(Φ))]  (12)

At the completion of such a second incremental move, with the exceptionof errors due to bending variations in fiducial plate 122 over the arrayof probes 133, the full desired overtravel may be achieved.

Probe Card and Fixture Deflection

In accordance with some embodiments, deflection effects caused bydeflection or other deformation of probe card 132, of fixture 131, or ofboth may be considered. Assuming no a priori knowledge of the relativecompliance of the two foregoing components, the compliance effects ofeach may be combined together, and therefore a combined card/fixturedeflection measurement may be obtained.

In one exemplary embodiment, the relationship between measured opticalplanarity and electrical planarity may be expressed generally as setforth below in Equation (13):p _(einb) =p _(oinb)+δ_(ginb)+δ_(cfinb)+δ_(sinb)  (13)

The quantities p_(einb) and p_(oinb) represent the electrical andoptical planarity, respectively, at a non-bussed probe, i_(nb). Theremaining three terms, δ_(ginb), δ_(cfinb), and δ_(sinb), represent thedeflection of fiducial plate 122, the combined probe card/fixturedeflection, and the deflection of z-stage 140, respectively, at anon-bussed probe, i_(nb), at the time of its first electrical contact.As set forth in detail above with specific reference to FIG. 2, the termδ_(sinb) may be made effectively zero, for example, using appropriatez-sensor data from a suitable location.

Solving for the card/fixture deflection, δ_(cfinb), in Equation (13)yields:δ_(cfinb) =p _(einb) −p _(oinb)−δ_(ginb)−δ_(sinb)  (14)

The sole unknown term in Equation (14) is the deflection in fiducialplate 122 at first electrical contact, δ_(ginb). The present disclosurecontemplates several mechanisms for measuring or estimating this firsttouch plate deflection, δ_(ginb).

The most direct method of computing δ_(ginb) is to adjust opticalassembly 150 to image directly opposite each probe 133 as it makescontact with fiducial plate 122, and to measure the deflection offiducial plate 122 at that point. This approach, however, comes at theexpense of both complexity and time, as two-dimensional motion of opticsassembly 150 (in both the x and y directions), fiducial plate 122, orboth, is required accurately to position optics assembly 150 and tomeasure the deflection of fiducial plate 122 at each probe 133 as itcomes into first contact.

Another approach for computing δ_(ginb) is based upon an assumption thatloading of fiducial plate 122, both with respect to forces and to rolland pitch moments, may be treated as approximately linear with totalcumulative probe overtravel. In this context, the term “total cumulativeprobe overtravel” generally refers to the sum of all the overtravelcomponents (each of which may be respectively attributable to eachindividual probe 133) from respective first touch to the currentposition. For most probe cards under typical probe to fiducial plateleveling conditions, this assumption of linear total cumulative loadingis a good assumption. One notable exception arises in the case of probecards utilizing vertical buckle beam technology, but even thistechnology has linearly increasing loads from first touch to the pointjust prior to buckling.

Given the foregoing linearity assumption, the first touch fiducial platedeflection may be calculated as a function of full overtravel fiducialplate deflection, δ_(gfinb), at a particular probe (i_(nb)) andknowledge of the optical planarity, p_(oinb).

Initially, the total cumulative overtravel from first touch to the finalovertravel position may be determined in accordance with Equation (15):

$\begin{matrix}{{OT}_{total} = \left\{ \begin{matrix}{{\sum\limits_{i = 0}^{n}z_{final}} - p_{0_{i}}} & {{{linear}\mspace{14mu}{technology}}\mspace{70mu}} \\{\sum\limits_{i = 0}^{n}\;{\min\left( {{z_{final} - p_{0_{i}}},\delta_{z_{buckle}}} \right)}} & {{buckle}\mspace{14mu}{beam}\mspace{14mu}{technology}}\end{matrix} \right.} & (15)\end{matrix}$where the quantity z_(final) generally represents the final overtravelposition as determined by Equation (10) set forth above, and thequantity δ_(zbuckle) generally represents the probe buckling distance.Then, for every probe, i, the total linear overtravel required to reachit from first touch is given by Equation (16) set forth below. In thiscontext, “total linear overtravel” refers to the total overtraveldistance over which the loads are linearly increasing with displacement.

$\begin{matrix}{{OT}_{i} = \left\{ \begin{matrix}{\sum\limits_{j = 1}^{n}{\max\;\left( {{p_{0_{i}} - p_{0_{j}}},0} \right)}} & {{{linear}\mspace{14mu}{technology}}\mspace{70mu}} \\{\sum\limits_{j = 1}^{n}\;{\min\left( {{\max\;\left( {{p_{0_{i}} - p_{0_{j}}},0} \right)}\;,\delta_{z_{buckle}}} \right)}} & {{buckle}\mspace{14mu}{beam}\mspace{14mu}{technology}}\end{matrix} \right.} & (16)\end{matrix}$

Under the assumption of load linearity with cumulative overtravel, thefiducial plate deflection at first touch is simply expressed as thefiducial plate deflection at full overtravel multiplied by the ratio ofthe cumulative overtravel to first touch to the total cumulativeovertravel. This is expressed mathematically as set forth below inEquation (17):δ_(ginb)=δ_(gfinb)(OT _(inb) /OT _(total))  (17)

Given Equation (14), the combined card/fixture deflection at everynon-bussed probe, i_(nb), may be computed. Fixture deflection at otherlocations can readily be determined and quantified by two dimensionalinterpolation.

Load Compensated Optical Planarity

Equation (13) sets forth a relationship between electrical and opticalplanarity. This equation allows loaded planarity to be calculated. Bytaking the measured optical planarity for a given probe and adding thefirst touch card/fixture deflection observed at that probe, theequivalent loaded planarity may be expressed as indicated in Equation(18):p _(1i) =p _(oi)+δ_(cf)(x _(i) , y _(i))  (18)

The term δ_(cf) (x_(i), y_(i)) in Equation (18) requires a twodimensional interpolation to evaluate. This interpolation to modelcharacteristics at the location of a probe, i, may be performed on theordered triplet of data (x_(inb), y_(inb), δ_(cfinb)) evaluated at apoint (x_(i), y_(i)).

FIG. 5 is a simplified flow diagram illustrating the general operationof one embodiment of a method of obtaining planarity measurements in aprobe card analysis system. As indicated at the center of FIG. 5, anexemplary method of obtaining planarity measurements may generallycomprise computing or accounting for stage deflection effects (block510), computing or accounting for fiducial plate deflection effects(block 520), computing or accounting for probe card and probe fixturedeflection effects (block 530), and computing load compensated planarity(block 540).

One exemplary mechanism for mitigating stage deflection effectscontributing to planarity errors employs a direct measurement acquiredas close as possible to the fiducial plate and to the probe cardfixture, i.e., acquiring stage deflection measurements at proximalsensor locations, where “proximal” in this context generally refers tothe vicinity of the fiducial plate and the probe card fixture wherestage deflection is most likely to occur. Applications employing anappropriately disposed direct measurement sensor were described abovewith specific reference to FIGS. 1 and 2. As indicated at block 511,accounting for planarity effects due to stage deflection may compriseutilizing a distance sensor (e.g., z-sensor 141 in the FIG. 2embodiment) proximate to the stage deflection.

Various methods of computing fiducial plate deflection effects such asdepicted at block 520 are set forth in detail above with specificreference to FIGS. 3 and 4. Specifically, the operation at block 520represents a process by which the amount of deflection that has occurredin the area of the fiducial plate that contacts the array of probes maybe accurately measured.

As set forth above, optical analyses for measuring fiducial platedeflection (block 521) may involve acquiring image data of one or morefiducials in a grid or predetermined pattern on the fiducial plate(block 522). The image data acquisition process depicted at block 522may employ a CCD or CMOS device, for example, and may additionallyrequire or benefit from other optical components. In some embodiments,image data may be acquired from different perspectives, such as from twoor more perspectives, and under different load conditions, such as aloaded condition and a no-load condition. In particular, the imagingoperation at block 522 may result in acquisition of visual or otherimage data of the fiducial grid in a no-load condition and in a loadedcondition, wherein each condition is imaged from two perspectives.Accordingly, measurements may be taken of the grid structure underdiffering conditions and from multiple imaging perspective.

The foregoing measurements may be employed to compute deflection, pitch,and roll of the fiducial plate (block 523) which may be compensated, forexample, with a first order correction (block 524) as set forth abovewith particular reference to Equations 1–5. The dashed arrow from block524 back to block 520 is intended to indicate that accounting forfiducial plate deflections may terminate at block 524, i.e., second orhigher order corrections may be neither required nor desired.Deflection, pitch, and roll rates for the fiducial plate (block 525) mayadditionally be computed, allowing a second order correction (block 526)as set forth above with reference to Equations 6–12. Those of skill inthe art will appreciate that the exemplary computations set forth hereinare susceptible of numerous modifications and may be altered orinfluenced by, for example, overall system configuration and mechanicalprecision, resolution of the imaging apparatus employed, computationalcapabilities of data processing components, desired accuracy ofcorrections, and other factors. Corrections beyond the second order arealso possible and may readily be implemented with appropriate hardwareand data processing capabilities.

As indicated in FIG. 5, computing or accounting for probe card and probecard fixture deflection effects (block 530) may generally compriseobtaining measurements of optical planarity and measurements ofelectrical planarity (block 531) for all non-bussed probes, identifyingfiducial plate deflection at first electrical contact (block 532) at allnon-bussed probe locations, and computing a combined deflection (block533) attributable to deflection of the probe card and deflection of theprobe card fixture. By way of example, the various operations depictedat blocks 530–533 may be executed substantially as set forth above withspecific reference to Equations 13–17.

Similarly, computing the load compensated planarity (block 540) may beexecuted substantially as described above. The relationship betweenelectrical and optical planarity, such as expressed in Equation (13),for example, may allow loaded planarity to be calculated as a functionof the measured optical planarity for a given probe and the first touchcard/fixture deflection observed at that probe.

Aspects of the present invention have been illustrated and described indetail with reference to particular embodiments by way of example only,and not by way of limitation. It will be appreciated that variousmodifications and alterations may be made to the exemplary embodimentswithout departing from the scope and contemplation of the presentdisclosure. It is intended, therefore, that the invention be consideredas limited only by the scope of the appended claims

1. A method of obtaining planarity measurements in a probe card analysissystem; said method comprising: computing planarity effects due tofiducial plate deflection; combining planarity effects due to probe carddeflection and due to probe card fixture deflection; and responsive tosaid computing and said combining, calculating a load compensatedplanarity for said probe card.
 2. The method of claim 1 furthercomprising accounting for planarity effects due to stage deflection andwherein said calculating is further responsive to said accounting. 3.The method of claim 2, wherein said accounting comprises utilizing adistance sensor proximate to said stage deflection.
 4. The method ofclaim 1 wherein said computing comprises utilizing an optical metrologytechnique.
 5. The method of claim 4 wherein said utilizing an opticalmetrology technique comprises: acquiring image data of a fiducial onsaid fiducial plate; responsive to said acquiring, identifyingdeflection data values representative of a deflection of said fiducialplate; and responsive to said identifying, providing correction datavalues enabling a first order correction of said deflection.
 6. Themethod of claim 5 wherein said utilizing an optical metrology techniquefurther comprises: further identifying rate data values representativeof a rate of deflection of said fiducial plate; and responsive to saidfurther identifying, providing additional correction data valuesenabling a second order correction of said deflection.
 7. The method ofclaim 1 wherein said combining comprises: obtaining measurements ofoptical planarity and electrical planarity for said probe card;measuring fiducial plate deflection at first electrical contact; andresponsive to said obtaining and said measuring, computing a combineddeflection value for said probe card and said probe card fixture.